The agency extended the compliance due date to June 26, 2006.

MSHA announced on May 22 it would not approve any requests to construct alternative seals and that coal mine operators were required to immediately examine the structural integrity of all existing underground alternative seals as well as revise their ventilation plans to assess the mine atmosphere behind these seals.

The reassessment is to include mine methane liberation history, seam history (spontaneous combustion potential or seam liberation potential), mine ventilation experience and a proposed sampling regime.

MSHA said the sampling regime should include a description of how sealed atmospheres would be sampled, such as in-mine sampling, through boreholes from either the mine surface or by other means.

MSHA said in addition, the plan should propose remedial actions to be taken if the atmosphere in a sealed area is found to be in the explosive range. Atmospheres found to be near the explosive range when considering barometric pressure changes and other factors, such as temperature and accumulations of water, could also require remedial action.

Remedial actions could include inert gas injection or the use of water to inert the area if the mine dip and other conditions are conducive to this type of action. In some cases, resealing, grout injection or other remedial measures may be necessary to provide protective isolation of the sealed area.

The moratorium and reassessment of existing seals follow the two recent and deadly mine explosions at the Sago Mine in January 2006 and the Darby No. 2 Mine in May 2006, where investigations show that there were problems with the use of alternative methods and materials to create seals.